Vehicles may include cooling systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the engine, the heated coolant then circulated through a radiator to dissipate the heat. The cooling system may include various components such as a coolant reservoir coupled to the system for degassing and storing coolant. A pressurized reservoir that also serves to separate entrained air from the coolant is typically called a degas bottle. When the temperature of coolant anywhere in the system rises, thermal expansion of the coolant causes pressure to rise in the degas bottle as the trapped air volume reduces. Pressure relief can be achieved by releasing air from the degas bottle through a valve that is typically mounted in the fill cap. Then, when the temperature and pressure of coolant drops below atmospheric pressure in the degas bottle, air may be drawn back into the bottle through another valve that is often mounted in the fill cap.
If the coolant level in bottle is too low, the air volume will be too large to build sufficient pressure to prevent boiling and cavitation at the water pump inlet. At low fluid levels, the degas bottle will also no longer be able to separate air from the coolant and air can be drawn into the cooling system, again leading to poor cooling performance. If an overflow system is employed instead of an active degas system, a similar loss in cooling system performance can be realized when fluid levels are low.
Various approaches may be used to estimate fluid level in a reservoir. One example approach described by Murphy in U.S. Pat. No. 8,583,387 uses an ultrasonic fluid level sensor installed at the bottom of a reservoir to estimate a fluid level of the reservoir. However, the inventors herein have recognized that in such a cooling system, the dimensions of the coolant reservoir may vary based on the temperature of coolant contained in the reservoir. As a result, there may be inconsistencies in the estimated coolant level. Additionally, due to the location of the sensor at the bottom of the container, at low coolant levels, it may be unclear whether the fluid level in the reservoir is low or empty. Further still, it may be difficult to differentiate actual low coolant levels from incorrect coolant level estimation due to sensor degradation. In another example approach, described by Gordon et al in US 20130103284, the sensor is coupled to a coolant reservoir hose. One issue with such an approach is that the sensor can only detect the presence of coolant at that location in the circuit. Critical components of the power train may not be receiving coolant despite the presence of coolant in one of the coolant reservoir hoses, particularly if that hose is isolated from the cooling system by a valve (e.g., the engine thermostat hose). Further, while an indication of low coolant fluid level is received, engine temperature control may already be degraded due to substantial emptying of the coolant reservoir.
In one example, some of the above issues may be addressed by an engine coolant system, comprising: a coolant overflow container having an internal recess to hold fluid; a vertical, hollow tube positioned external to the container and including an internal recess to hold fluid, a bottom-most level of the recess positioned vertically below a bottom-most level of the internal recess of the container; and a sensor coupled to the bottom-most level of the internal recess of the tube. In this way, a coolant reservoir fluid level may be more reliably inferred based on the fluid level of the vertical tube, reducing the likelihood of engine overheating.
As an example, an engine cooling system may include a degas bottle for separating entrained air from coolant and regulating system pressure. The degas bottle may be fluidically coupled to a vertical standpipe via top and bottom hoses wherein the top hose couples a topmost level of the standpipe to the top of the degas bottle and the bottom hose couples a bottom-most level of the standpipe to the bottom-most level of the degas bottle. The bottom of the vertical pipe may be positioned below the bottom of the degas bottle so that a lower threshold level of fluid trapped in the vertical pipe, measurable by a coolant level sensor, may indicate an almost empty degas bottle. The vertical pipe may comprise a material that is resistant to thermal expansion so that the dimensions of the pipe do not vary with coolant temperature. During vehicle motion, fluid may transfer between the degas bottle and the standpipe. An ultrasonic sensor may be coupled in the standpipe within an internal recess at the bottom-most level of the standpipe. The sensor may include a processor for processing and output generated by the sensor locally, the processor further communicating the output with an engine controller. The sensor may be configured to intermittently transmit a series of ultrasonic pulses, at a predetermined frequency and energy output, towards the topmost level of the standpipe. In addition the sensor may be configured to receive an echo of the transmitted pulses following reflection of the pulses from the upper surface of the liquid. Based on a duration elapsed between the transmission of the pulses and the detection of the pulses, the local processor may estimate a height of fluid in the standpipe. Due to the unique configuration of the standpipe being fluidically coupled to the degas bottle at both topmost and bottom-most locations, fluid levels may equilibrate between the standpipe and the degas bottle. Therefore, in addition to the standpipe fluid level being estimated using the sensor output, a bulk coolant level in the degas bottle may also be inferred based on the fluid level in the standpipe. An engine controller may compare the inferred bulk coolant level to one or more thresholds to estimate a state of the coolant level, and adjust engine operation in accordance.
In this way, an accuracy and reliability of determining a coolant level of a coolant overflow reservoir can be increased. By inferring the coolant level of the reservoir based on an estimated coolant level of a standpipe coupled to the reservoir, inaccuracies in coolant level estimation due to distortion of an in-tank sensor output during thermal fluctuations is reduced. By relying on an ultrasonic sensor and the local processor to estimate the coolant level of the standpipe based on an echo time, coolant level estimation can be expedited and better compensated for variations in fluid level due to coolant slosh. Overall, engine overheating due to inaccurate coolant level estimation can be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.